4-aminodiphenylamine (4-ADPA) is an important starting product for the synthesis of antioxidants and stabilizers in the rubber and polymer industry (Kirk-Othmer, Encyclopedia of Chemical Technology, 4.sup.th Edition, 1992, Vol. 3, page 424-456; Ullmann's Encyclopedia of Industrial Chemistry, 5.sup.th Edition, Vol. A3, 1985, pages 91-111).
4-ADPA may be produced by various methods. One possible method of producing 4-ADPA is the two-stage reaction of aniline or aniline derivatives with p-nitrochloro-benzene in the presence of an acid acceptor or a neutralizing agent, optionally in the presence of a catalyst. Production by this method is described, for example, in DE-A 3,246,151, DE-A 3,501,698, DE-A 185663, U.S. Pat. Nos. 4,670,595, 4,187,249 and 4,187,248. The first stage is generally performed using copper catalysts, and the second stage is performed with different metal components, e.g. nickel (see for example U.S. Pat. No. 5,840,982). Reactions also of, for example, halogenated nitrobenzenes with amines in the presence of palladium catalysts are described in U.S. Pat. No. 5,576,460 and EP-A 846,676.
The disadvantage of the processes described in the above literature is frequently inadequate selectivity, in particular, during formation of the intermediate product, whereby yield losses occur as a result of more or less complex purification steps, before the 4-aminodiphenylamines may be formed by hydrogenation.